Re: [PATCH 2/2] drivers/dax: Changing RC value

2017-04-12 Thread Dan Williams 
On Tue, Apr 11, 2017 at 1:58 PM, Andrew Morton
 wrote:
> On Tue, 11 Apr 2017 10:56:45 +0530 Pushkar Jambhlekar  
> wrote:
>
>> Changing rc value from VM_FAULT_FALLBACK to VM_FAULT_SIGBUS for an unknown / 
>> unsupported fault size.
>>
>> ...
>>
>> --- a/drivers/dax/dax.c
>> +++ b/drivers/dax/dax.c
>> @@ -590,7 +590,7 @@ static int dax_dev_huge_fault(struct vm_fault *vmf,
>>   rc = __dax_dev_pud_fault(dax_dev, vmf);
>>   break;
>>   default:
>> - rc =  VM_FAULT_FALLBACK;
>> + rc = VM_FAULT_SIGBUS;
>>   }
>>   rcu_read_unlock();
>
> The change seems to make sense but more info would be helpful.  What
> is wrong with the current code?  ie, what goes wrong if we return
> VM_FAULT_FALLBACK here?

Hi Andrew, I took these two patches into my for-4.12/dax branch with
the following fixed up changelog:

commit 17756a4c681c320712798b783eb40006de9b4cc3
Author: Pushkar Jambhlekar 
Date:   Tue Apr 11 09:12:25 2017 -0700

device-dax: fix dax_dev_huge_fault() unknown fault size handling

The default case for dax_dev_huge_fault() fault size handling mistakenly
returns when it should unlock. This is not a problem in practice since
the only three possible fault sizes are handled. Going forward, if the
core mm adds a new fault size beyond pte, pmd, or pud device-dax should
abort VM_FAULT_SIGBUS requests not VM_FAULT_FALLBACK since device-dax
guarantees a configured fault granularity for all faults.

Signed-off-by: Pushkar Jambhlekar 
Signed-off-by: Dan Williams 

diff --git a/drivers/dax/dax.c b/drivers/dax/dax.c
index 19795eb35579..94036d92ed16 100644
--- a/drivers/dax/dax.c
+++ b/drivers/dax/dax.c
@@ -591,7 +591,7 @@ static int dax_dev_huge_fault(struct vm_fault *vmf,
rc = __dax_dev_pud_fault(dax_dev, vmf);
break;
default:
-   return VM_FAULT_FALLBACK;
+   rc = VM_FAULT_SIGBUS;
}
srcu_read_unlock(_srcu, id);

Re: [PATCH 2/2] drivers/dax: Changing RC value

2017-04-12 Thread Dan Williams 
On Tue, Apr 11, 2017 at 1:58 PM, Andrew Morton
 wrote:
> On Tue, 11 Apr 2017 10:56:45 +0530 Pushkar Jambhlekar  
> wrote:
>
>> Changing rc value from VM_FAULT_FALLBACK to VM_FAULT_SIGBUS for an unknown / 
>> unsupported fault size.
>>
>> ...
>>
>> --- a/drivers/dax/dax.c
>> +++ b/drivers/dax/dax.c
>> @@ -590,7 +590,7 @@ static int dax_dev_huge_fault(struct vm_fault *vmf,
>>   rc = __dax_dev_pud_fault(dax_dev, vmf);
>>   break;
>>   default:
>> - rc =  VM_FAULT_FALLBACK;
>> + rc = VM_FAULT_SIGBUS;
>>   }
>>   rcu_read_unlock();
>
> The change seems to make sense but more info would be helpful.  What
> is wrong with the current code?  ie, what goes wrong if we return
> VM_FAULT_FALLBACK here?

Hi Andrew, I took these two patches into my for-4.12/dax branch with
the following fixed up changelog:

commit 17756a4c681c320712798b783eb40006de9b4cc3
Author: Pushkar Jambhlekar 
Date:   Tue Apr 11 09:12:25 2017 -0700

device-dax: fix dax_dev_huge_fault() unknown fault size handling

The default case for dax_dev_huge_fault() fault size handling mistakenly
returns when it should unlock. This is not a problem in practice since
the only three possible fault sizes are handled. Going forward, if the
core mm adds a new fault size beyond pte, pmd, or pud device-dax should
abort VM_FAULT_SIGBUS requests not VM_FAULT_FALLBACK since device-dax
guarantees a configured fault granularity for all faults.

Signed-off-by: Pushkar Jambhlekar 
Signed-off-by: Dan Williams 

diff --git a/drivers/dax/dax.c b/drivers/dax/dax.c
index 19795eb35579..94036d92ed16 100644
--- a/drivers/dax/dax.c
+++ b/drivers/dax/dax.c
@@ -591,7 +591,7 @@ static int dax_dev_huge_fault(struct vm_fault *vmf,
rc = __dax_dev_pud_fault(dax_dev, vmf);
break;
default:
-   return VM_FAULT_FALLBACK;
+   rc = VM_FAULT_SIGBUS;
}
srcu_read_unlock(_srcu, id);

Re: [PATCH 2/2] drivers/dax: Changing RC value

2017-04-11 Thread Andrew Morton 
On Tue, 11 Apr 2017 10:56:45 +0530 Pushkar Jambhlekar  
wrote:

> Changing rc value from VM_FAULT_FALLBACK to VM_FAULT_SIGBUS for an unknown / 
> unsupported fault size.
> 
> ...
>
> --- a/drivers/dax/dax.c
> +++ b/drivers/dax/dax.c
> @@ -590,7 +590,7 @@ static int dax_dev_huge_fault(struct vm_fault *vmf,
>   rc = __dax_dev_pud_fault(dax_dev, vmf);
>   break;
>   default:
> - rc =  VM_FAULT_FALLBACK;
> + rc = VM_FAULT_SIGBUS;
>   }
>   rcu_read_unlock();

The change seems to make sense but more info would be helpful.  What
is wrong with the current code?  ie, what goes wrong if we return
VM_FAULT_FALLBACK here?

Re: [PATCH 2/2] drivers/dax: Changing RC value

2017-04-11 Thread Andrew Morton 
On Tue, 11 Apr 2017 10:56:45 +0530 Pushkar Jambhlekar  
wrote:

> Changing rc value from VM_FAULT_FALLBACK to VM_FAULT_SIGBUS for an unknown / 
> unsupported fault size.
> 
> ...
>
> --- a/drivers/dax/dax.c
> +++ b/drivers/dax/dax.c
> @@ -590,7 +590,7 @@ static int dax_dev_huge_fault(struct vm_fault *vmf,
>   rc = __dax_dev_pud_fault(dax_dev, vmf);
>   break;
>   default:
> - rc =  VM_FAULT_FALLBACK;
> + rc = VM_FAULT_SIGBUS;
>   }
>   rcu_read_unlock();

The change seems to make sense but more info would be helpful.  What
is wrong with the current code?  ie, what goes wrong if we return
VM_FAULT_FALLBACK here?

[PATCH 2/2] drivers/dax: Changing RC value

2017-04-10 Thread Pushkar Jambhlekar 
Changing rc value from VM_FAULT_FALLBACK to VM_FAULT_SIGBUS for an unknown / 
unsupported fault size.

Signed-off-by: Pushkar Jambhlekar 
---
 drivers/dax/dax.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/dax/dax.c b/drivers/dax/dax.c
index fd9c4db..6156fdc 100644
--- a/drivers/dax/dax.c
+++ b/drivers/dax/dax.c
@@ -590,7 +590,7 @@ static int dax_dev_huge_fault(struct vm_fault *vmf,
rc = __dax_dev_pud_fault(dax_dev, vmf);
break;
default:
-   rc = VM_FAULT_FALLBACK;
+   rc = VM_FAULT_SIGBUS;
}
rcu_read_unlock();
 
-- 
2.7.4

[PATCH 2/2] drivers/dax: Changing RC value

2017-04-10 Thread Pushkar Jambhlekar 
Changing rc value from VM_FAULT_FALLBACK to VM_FAULT_SIGBUS for an unknown / 
unsupported fault size.

Signed-off-by: Pushkar Jambhlekar 
---
 drivers/dax/dax.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/dax/dax.c b/drivers/dax/dax.c
index fd9c4db..6156fdc 100644
--- a/drivers/dax/dax.c
+++ b/drivers/dax/dax.c
@@ -590,7 +590,7 @@ static int dax_dev_huge_fault(struct vm_fault *vmf,
rc = __dax_dev_pud_fault(dax_dev, vmf);
break;
default:
-   rc = VM_FAULT_FALLBACK;
+   rc = VM_FAULT_SIGBUS;
}
rcu_read_unlock();
 
-- 
2.7.4

[PATCH 2/2] drivers/dax: Changing RC value

2017-04-10 Thread Pushkar Jambhlekar 
Changing rc value from VM_FAULT_FALLBACK to VM_FAULT_SIGBUS for an unknown / 
unsupported fault size.

Signed-off-by: Pushkar Jambhlekar 
---
 drivers/dax/dax.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/dax/dax.c b/drivers/dax/dax.c
index fd9c4db..6156fdc 100644
--- a/drivers/dax/dax.c
+++ b/drivers/dax/dax.c
@@ -590,7 +590,7 @@ static int dax_dev_huge_fault(struct vm_fault *vmf,
rc = __dax_dev_pud_fault(dax_dev, vmf);
break;
default:
-   rc = VM_FAULT_FALLBACK;
+   rc = VM_FAULT_SIGBUS;
}
rcu_read_unlock();
 
-- 
2.7.4

[PATCH 2/2] drivers/dax: Changing RC value

2017-04-10 Thread Pushkar Jambhlekar 
Changing rc value from VM_FAULT_FALLBACK to VM_FAULT_SIGBUS for an unknown / 
unsupported fault size.

Signed-off-by: Pushkar Jambhlekar 
---
 drivers/dax/dax.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/dax/dax.c b/drivers/dax/dax.c
index fd9c4db..6156fdc 100644
--- a/drivers/dax/dax.c
+++ b/drivers/dax/dax.c
@@ -590,7 +590,7 @@ static int dax_dev_huge_fault(struct vm_fault *vmf,
rc = __dax_dev_pud_fault(dax_dev, vmf);
break;
default:
-   rc = VM_FAULT_FALLBACK;
+   rc = VM_FAULT_SIGBUS;
}
rcu_read_unlock();
 
-- 
2.7.4